<!DOCTYPE html>
<html>
	<script>
		function Universe() {
			if ( typeof Universe.instance === 'object') {
				return Universe.instance;
			}
			this.a = '单体';
			Universe.instance = this;
		}

		alert(Universe.instance) //true
		var uni = new Universe();
		alert(Universe.instance) //true
	</script>
</html>